Geralf, the Fleshwright

Whenever you cast a spell during your turn other than your first spell that turn, create a 2/2 blue and black Zombie Rogue creature token.
Whenever a Zombie you control enters, put a +1/+1 counter on it for each other Zombie that entered the battlefield under your control this turn.

Outlaws of Thunder Junction

Whenever you cast a spell during your turn other than your first spell that turn, create a 2/2 blue and black Zombie Rogue creature token.
Whenever a Zombie enters the battlefield under your control, put a +1/+1 counter on it for each other Zombie that entered the battlefield under your control this turn.

Outlaws of Thunder Junction Promos

Geralf’s first ability will consider spells you cast before it was on the battlefield. For example, if Geralf is the first spell you cast during your turn, each subsequent spell you cast that turn after it’s on the battlefield will cause its first ability to trigger.

If multiple Zombies enter the battlefield under your control at the same time, Geralf’s last ability will trigger for each of those Zombies. Each of those triggered abilities will see each of those other Zombies that entered the battlefield plus any other Zombies that entered the battlefield under your control so far this turn.